Run the equator: September 2009

Saturday, September 26, 2009

When your fuel pump goes...

I knew it had to happen to me sooner or later, and it did: as I left the grocery store heading home, my 21-year-old BMW did not start. A nice lady asked me if I needed help to jump the car, and I had to decline her offer; it wasn’t the battery, it had to be something else. Good thing the store was only a few blocks away from home. I had the car towed the next day, pushed it into my garage and started debugging.

There’s a straightforward step-by-step procedure you can follow to find the cause of a non-start. After eliminating the obvious suspects – a dead battery and the absence of spark – the most obvious component that needs to be tested is the fuel pump. In later E30 models (starting with production month 9/87) there is only a single fuel pump, located in the fuel tank, accessible through a hatch under the passenger’s side rear seat. It’s easy to check if the pump is working: remove the rear seat, remove the pump cover, crank up the car (or have a helper turn the key instead) and listen. The pump should make… well, pumping sounds, just as you imagine a fuel pump would sound. If you can’t hear anything it could mean that:

  1. Either the pump is broken and you need a new one, or
  2. You have no voltage at the pump – because either the wires are interrupted (pray that they aren’t because fixing wiring in a car is a terrible job) or your fuel pump relay is bad

To check for voltage remove the power connector from the pump, stick the probes of a voltmeter in the connector and crank the car – if the relay works the probe should show battery voltage, about 12V. Operating the ignition while holding the probe in the connector and reading the voltmeter display can be a pretty cumbersome task - another set of hands greatly helps. If you’re working alone you can simplify your life if you bypass the relay: remove it from its socket and link the connector’s pins 30 and 87 together with a wire (preferably a fuse holder with a 15amp fuse); this will bypass the ignition and supply constant battery power to the fuel pump (that’s also a good way to make sure the wiring is fine).

If there’s voltage at the fuel pump but the pump is silent it’s time for a new pump. There are a few models for sale that can fit the E30. The OEM pump for the ’88 E30 is a VDO. The good thing about it is that it comes with the complete assembly: fuel pump, mounting frame, filter and O-ring; you just swap the old one out and re-connect the hose. The average price online for this OEM part is about $200. The cheapest I could find it for was $176.35 at Unexpectedly, my usual supplier sells the VDO pump for an ungodly $362.95.

The TRE 340 in a box
The alternative is a pump from an aftermarket supplier like TRE or Walbro. The TRE 340 had good reviews (if you can ever take seriously anything you read on internet forums) and it’s for sale on eBay. The noticeable price difference ($78.98, shipping included) tipped the balance in its favor. However, generic aftermarket pumps come with a catch – they require some wiring work, and they may need modifications to the fuel pump assembly to fit.

This is the whole procedure, step by step. Click on each picture to see a larger version and access the image notes. Click here for the whole set.

The Bentley recommends disconnecting the battery (as it does for almost every procedure); I didn’t. Anyway, be careful when you work around fuel lines. Don’t smoke.

Remove the rear seat and then unscrew the four bolts that hold the black oval access cover on the passenger’s side. There’s a similar round cover on the driver’s side – that’s just a fuel gauge sending unit; leave it alone.

Remove the electrical connectors: the connector with 2 pins is the power supply. The other is the fuel gauge sender connector.

Loosen the hose clamp and remove the hose. Either end will do. The one on the fuel-line side was easier to remove. Fuel may be discharged – in my case there wasn’t any fuel in the line since the pump was broken.

Remove the four 8mm mounting screws on top of the fuel gauge sending unit.

Pull the sending unit out of the tank. Wait until all the liquid drips back in the tank. There is a lot of gas in the can, and it all drips out through a tiny hole at the bottom.

Rotate the fuel pump assembly counter-clockwise to loosen it.

Remove fuel pump assembly out of the tank. Make a note of the position of the assembly when it comes out. You will have to put it in the same way.

Look at the assembly and notice the alignment of the fuel filter relative to the frame. You will need to install the new filter in the same position.

Remove the filter by pulling on it, and then remove the pump from the frame. The connector wires are soldered to the assembly. You will have to melt the solder or cut the wires.

There’s an obvious size difference between the old pump and the new. Fit the sleeves that came in the package around the new pump - it will increase its diameter and make it fit snugly in the frame. The sleeves are optional.

The short feeding tube at the bottom of the TRE pump and the similar tube on the OEM pump have different diameters and are positioned differently. To make the new pump fit we have to tinker a bit with the assembly frame.

Carefully carve in the bottom support of the frame until the feeding tube of the new pump can fit through. Be mindful not to damage the frame too much. Either way, it’s not going to look pretty, but who cares – it goes in the tank!

Solder the connector wires that came in the package to the terminal pins on the frame. I wasn’t very good at that job. I hadn’t soldered anything since shop class in school. So far I’ve used butt connectors for all the electrical work on this car.

Use the short fuel hose (came with the package) to connect the pump’s outlet and the metal tube which is part of the assembly.

Pressing gently against the pump’s bottom tube install the filter maintaining the same orientation that the original filter had. I also strapped the pump to the frame with a zip-tie although it wasn’t strictly necessary; the pump was snug enough in place.

Insert the whole assembly with the new O-ring back in the tank. I couldn’t find an O-ring of the same size in any automotive shop and the local BMW dealer didn’t have one in stock so I decided to re-use the old O-ring. Let posterity judge me…

Reconnect and install the other pieces in the order they were disassembled.

Work time: about three hours.

After I completed the procedure, the car started immediately, as expected. I have not noticed any unpleasant noise when the pump is in operation. Now I can only hope that this new pump will last as long as the original one did...

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